Plasma processing apparatus

ABSTRACT

A plasma processing apparatus capable of optimizing a plasma process is provided. The plasma processing apparatus includes a control unit for controlling a minimum energy and a maximum energy of ions incident onto a substrate independently of each other such that ion energy of the ions are concentrated at a first energy band and a second energy band respectively. In the plasma processing apparatus, the oxide film is etched to form a hole within the oxide film, the first energy band is lower than a first energy value at which the oxide film is etched while the organic film is not etched, and the second energy band is higher than a second energy value at which an etching yield at an inclined surface of the hole is higher than an etching yield of an upper surface of the organic film.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of U.S. patent application Ser. No.13/214,372, filed on Aug. 22, 2011 which claims the benefit of JapanesePatent Application Nos. 2010-186017 and 2011-171005 filed on Aug. 23,2010 and Aug. 4, 2011, respectively, and U.S. Provisional ApplicationSer. No. 61/382,552, filed on Sep. 14, 2010, the entire disclosures ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The present disclosure relates to a technology of performing a plasmaprocess onto a target substrate, and to be specific, the presentdisclosure relates to a plasma processing apparatus capable of applyinga high frequency power for attracting ions toward a substrate positionedin a plasma space.

BACKGROUND OF THE INVENTION

In an etching process, a deposition process, an oxidation process, or asputtering process for manufacturing a semiconductor device or a FPD(Flat Panel Display), there has been used plasma in order to make aneffective reaction of a processing gas at a relatively low temperature.In such a plasma process, there has been used a high frequency power(RF) or a microwave in order to discharge or ionize a processing gaswithin a vacuum processing chamber.

By way of example, in a capacitively coupled plasma processingapparatus, an upper electrode and a lower electrode are arranged inparallel with each other within a processing chamber. Further, a targetsubstrate (a semiconductor wafer, a glass substrate or the like) ismounted on the lower electrode, and a high frequency power having afrequency (typically, about 13.56 MHz or higher) suitable for generatingplasma is applied to the upper electrode or lower electrode. A highfrequency electric field generated between the electrodes facing eachother by applying the high frequency power accelerates electrons, andplasma is generated by a collision and ionization between the electronsand a processing gas. Further, by a gas phase reaction or a surfacereaction of radicals or ions contained in the plasma, a thin film isdeposited on the substrate, or a material or a thin film on a surface ofthe substrate is etched.

As described above, radicals and ions incident onto a substrate may bean important factor in a plasma process. In particular, the ions areimportant in that the ions have a physical action by an impact when theions are incident onto the substrate.

Conventionally, in a plasma process, there has often used a RF biasmethod. In a RF bias method, a high frequency power having a relativelylow frequency (typically, about 13.56 MHz or lower) is applied to alower electrode for mounting thereon a substrate. Also, ions containedin plasma are accelerated by a negative bias voltage or a sheath voltagegenerated on the lower electrode, and are attracted to the substrate. Inthis way, the ions in the plasma are accelerated and the ions collidewith a surface of the substrate, so that a surface reaction, ananisotropic etching process or a film modification (film reform) can bepromoted.

-   Patent Document 1: Japanese Patent Laid-open Publication No.    H7-302786

In a conventional plasma processing apparatus having the above-describedRF bias function, only one kind (a single frequency) of a high frequencypower for attracting ions applied to a lower electrode is used. Further,this high frequency power, and a self-bias voltage or a sheath voltageon the lower electrode are used as control parameters.

However, as a result of repeated experiments on an action of RF biasconducted by the present inventors during a development in a technologyof a plasma process, it has been found that it is difficult to controlan ion energy distribution in a high-tech plasma process of multipleprocess characteristics by a conventional method using a single highfrequency power for attracting ions.

To be more specific, as a result of analyzing an energy distribution ofions (IED: Ion Energy Distribution) incident onto a substrate when asingle high frequency power for attracting ions is used, as depicted inFIGS. 19A to 19C and 20A to 20C, energy of all incident ions isregularly distributed in a continuous energy band, and lots of ions areconcentrated (peaks are shown) in a vicinity of the maximum energy andin a vicinity of the minimum energy. Therefore, if it is possible toreadily vary not only an average value of ion energy but also themaximum energy and minimum energy on which the ions are concentrated, itis expected that a RF bias function required for a plasma process can beeffectively controlled. However, it is deemed that this is notavailable.

In accordance with a conventional method, when a high frequency powerhaving a relatively low frequency of, for example, about 0.8 MHz is usedfor attracting ions, if a RF power is varied, an ion energy distributioncharacteristic is varied as shown in FIG. 19A (low power), FIG. 19B(intermediate power), and FIG. 19C (high power). That is, while theminimum energy is fixed to about 0 eV, the maximum energy is varied intoabout 1000 eV (FIG. 19A), about 2000 eV (FIG. 19B), and about 3000 eV(FIG. 19C) in proportion to the RF power.

However, when a high frequency power having a relatively high frequencyof, for example, about 13 MHz is used for attracting ions, if a RF poweris varied, an ion energy distribution characteristics is varied as shownin FIG. 20A (low power), FIG. 20B (intermediate power), and FIG. 20C(high power). That is, while the maximum energy is varied into about 650eV, about 1300 eV, and about 1950 eV in proportion to the RF power, theminimum energy is also varied into about 350 eV, about 700 eV, and about1050 eV in proportion to the RF power.

Although FIGS. 19A to 19C and 20A to 20C show ion energy distributioncharacteristics of argon (Ar⁺) ions, other ions may have the samecharacteristics (patterns).

As described above, in the conventional method, even if the maximumenergy or average energy in an ion energy distribution can be varied,the minimum energy cannot be varied independently of the maximum energy.Therefore, it is impossible to achieve an ion energy distributioncharacteristic indicated by, for example, a virtual line (a dasheddotted line) K in FIG. 20C. Accordingly, as also will be described inembodiments of the present disclosure, a trade-off between (an etchingrate and selectivity) and an etching profile in a HARC (High AspectRatio Contact) plasma etching process cannot be avoided readily.

BRIEF SUMMARY OF THE INVENTION

In order to solve the above-described conventional problems, the presentdisclosure provides a plasma processing method and a plasma processingapparatus capable of optimizing a plasma process in response to variousrequirements of a micro processing by effectively controlling a RF biasfunction.

In view of the foregoing, in accordance with one aspect of the presentdisclosure, there is provided a plasma processing method including:mounting a target substrate on a first electrode positioned within anevacuable processing chamber; generating plasma by exciting a processinggas within the processing chamber; applying to the first electrode afirst high frequency power and a second high frequency power each havinga different frequency in order to attract ions from the plasma towardthe substrate; and performing a plasma process on the substrate by theplasma. In performing a plasma process, a total power and a power ratioof the first and second high frequency powers are controlled to optimizeat least one process characteristic which is dependent on energy of ionsincident onto the substrate.

Further, in accordance with another aspect of the present disclosure,there is provided a plasma processing apparatus including an evacuableprocessing chamber for accommodating a target substrate andloading/unloading the substrate; a processing gas supply unit forsupplying a processing gas into the processing chamber; a plasmageneration unit for generating plasma of the processing gas within theprocessing chamber; a first electrode for mounting and holding thesubstrate thereon within the processing chamber; a first high frequencypower supply unit for applying to the first electrode a first highfrequency power having a first frequency in order to attract ions fromthe plasma toward the substrate on the first electrode; a second highfrequency power supply unit for applying to the first electrode a secondhigh frequency power having a second frequency higher than the firstfrequency in order to attract ions from the plasma toward the substrateon the first electrode; and a control unit for controlling a total powerand a power ratio of the first and second high frequency powers tooptimize at least one process characteristic dependent on energy of ionsincident onto the substrate from the plasma.

In accordance with the present disclosure, the first and second highfrequency powers having the first and second frequencies, respectively,appropriate for attracting ions are applied to the first electrode formounting thereon the target substrate, and a total power of the firstand second high frequency powers and a power ratio thereof are variablycontrolled. Therefore, in an energy distribution of ions incident ontothe substrate from the plasma, it is possible to control the minimumenergy and the maximum energy independently of each other. Further, itis also possible for an ion energy distribution characteristic to have aconcave shape or a flat shape. Accordingly, the ion energy distributioncharacteristic can be optimized with respect to various processcharacteristics, and also the process characteristics can be optimized.

In accordance with a plasma processing method and a plasma processingapparatus of the present disclosure, a RF bias function can beeffectively controlled by the above-described function and operation, sothat a plasma process can be optimized in response to variousrequirements of a micro processing.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments will be described inconjunction with the accompanying drawings. Understanding that thesedrawings depict only several embodiments in accordance with thedisclosure and are, therefore, not to be intended to limit its scope,the disclosure will be described with specificity and detail through useof the accompanying drawings, in which:

FIG. 1 is a cross-sectional view showing a configuration of a plasmaprocessing apparatus in accordance with an embodiment of the presentdisclosure;

FIG. 2 shows a waveform of a sheath voltage and an ion response voltagein a dual frequency RF bias method in the embodiment;

FIG. 3 shows a conversion function employed in the embodiment;

FIG. 4 shows an ion energy distribution and an ion response voltage in asingle frequency RF bias method;

FIG. 5 shows an ion energy distribution and an ion response voltage in adual frequency RF bias method;

FIG. 6A shows a function of adjusting the minimum energy of an ionenergy distribution within a certain range as desired while the maximumenergy is fixed in the embodiment;

FIG. 6B shows a function of adjusting the minimum energy of an ionenergy distribution within a certain range as desired while the maximumenergy is fixed;

FIG. 6C shows a function of adjusting the minimum energy of an ionenergy distribution within a certain range as desired while the maximumenergy is fixed;

FIG. 7A shows a function of adjusting the maximum energy of an ionenergy distribution within a certain range as desired while the minimumenergy is fixed in the embodiment;

FIG. 7B shows a function of adjusting the maximum energy of an ionenergy distribution within a certain range as desired while the minimumenergy is fixed;

FIG. 7C shows a function of adjusting the maximum energy of an ionenergy distribution within a certain range as desired while the minimumenergy is fixed;

FIG. 8A shows a function of varying a width of an energy band within acertain range as desired while a central value of energy is fixed in theembodiment;

FIG. 8B shows a function of varying a width of an energy band within acertain range as desired while a central value (an average value) ofenergy is fixed;

FIG. 8C shows a function of varying a width of an energy band within acertain range as desired while an average value of energy is fixed;

FIG. 8D shows a function of varying a width of an energy band within acertain range as desired while an average value of energy is fixed;

FIG. 8E shows a function of varying a width of an energy band within acertain range as desired while an average value of energy is fixed;

FIG. 9 is a diagram for explaining a combination of frequencies in adual frequency RF bias method of the embodiment;

FIG. 10 is a longitudinal cross-sectional view schematically showing anetching process in a HARC process;

FIG. 11A is a graph showing an etching rate and a thickness of a CFpolymer film when a flow rate of a C₄F₈ gas is changed in an etchingprocess for a SiO₂ film;

FIG. 11B is a graph showing an etching rate and a thickness of a CFpolymer film when a flow rate of a C₄F₈ gas is changed in an etchingprocess for a SiN film;

FIGS. 12A and 12B are longitudinal cross-sectional views eachschematically showing a necking in a HARC process;

FIGS. 13A and 13B show ion energy dependency of an etching yield of anoxide film and an organic film in a HARC process, and also show an ionenergy distribution characteristic by a conventional single frequency RFbias method;

FIGS. 14A and 14B show ion energy dependency of an etching yield of anoxide film and an organic film in a HARC process, and also show an ionenergy distribution characteristic by a dual frequency RF bias method ofthe embodiment;

FIG. 15 shows an incident angle when ions are incident onto eachposition of a mask (an organic film) in a HARC process;

FIG. 16 shows cross-sectional shapes of a pattern and characteristicdata obtained in a HARC process performed by a dual frequency RF biasmethod;

FIG. 17 shows (an enlarged view of) cross-sectional shapes of a patternand characteristic data obtained in a HARC process performed by a dualfrequency RF bias method;

FIG. 18 is a longitudinal cross-sectional view showing a configurationof a plasma processing apparatus in accordance with another embodiment;

FIG. 19A shows an ion energy distribution obtained by setting a RF powerto be low in a conventional signal frequency RF bias method using arelatively low frequency;

FIG. 19B shows an ion energy distribution obtained by setting a RF powerto be intermediate level in a conventional signal frequency RF biasmethod using a relatively low frequency;

FIG. 19C shows an ion energy distribution obtained by setting a RF powerto be high in a conventional signal frequency RF bias method using arelatively low frequency;

FIG. 20A shows an ion energy distribution obtained by setting a RF powerto be low in a conventional signal frequency RF bias method using arelatively high frequency;

FIG. 20B shows an ion energy distribution obtained by setting a RF powerto be intermediate level in a conventional signal frequency RF biasmethod using a relatively high frequency; and

FIG. 20C shows an ion energy distribution obtained by setting a RF powerto be high in a conventional signal frequency RF bias method using arelatively high frequency.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present disclosure will be described indetail with reference to FIGS. 1 to 18.

[Overall Configuration of Apparatus]

FIG. 1 shows a configuration of a plasma processing apparatus inaccordance with an embodiment of the present disclosure. This plasmaprocessing apparatus may be configured as a capacitively coupled plasmaetching apparatus in which two radio frequency powers are applied to alower electrode or a radio frequency power is applied to an upperelectrode. The plasma processing apparatus may include a cylindricalvacuum chamber (processing vessel) 10 made of, e.g., aluminum whosesurface is alumite-treated (anodically oxidized). The chamber 10 may beframe-grounded.

At a bottom of the chamber 10, a cylindrical susceptor support 14 may beprovided via an insulating plate 12 made of ceramic or the like, and onthe susceptor support 14, a susceptor 16 made of, for example, aluminummay be provided. The susceptor 16 may serve as a lower electrode and atarget substrate, for example, a semiconductor wafer W may be mountedthereon.

On an upper surface of the susceptor 16, an electrostatic chuck 18 forholding the semiconductor wafer W by electrostatic attracting force maybe provided. This electrostatic chuck 18 may include an electrode 20made of a conductive film embedded between a pair of insulating layersor insulating sheets, and the electrode 20 may be electrically connectedto a DC power supply 22 via a switch 24. With this configuration, thesemiconductor wafer W can be attracted to and held on the electrostaticchuck 18 by an electrostatic force caused by a DC voltage from the DCpower supply 22. Around the electrostatic chuck 18 and on the uppersurface of the susceptor 16, a focus ring 26 made of, for example,silicon may be positioned in order to enhance uniformity of an etchingprocess in the surface. To side surfaces of the susceptor 16 and thesusceptor support 14, a cylindrical inner wall member 28 made of, forexample, quartz may be secured.

Within the susceptor support 14, a coolant cavity or coolant path 30 of,e.g., a circular ring-shape may be formed. A coolant such as coolingwater cw of a certain temperature may be supplied into and circulatedthrough the coolant path 30 from an external chiller unit (notillustrated) via lines 32 a and 32 b. A processing temperature of thesemiconductor wafer W on the susceptor 16 can be controlled depending ona temperature of the coolant cw. Further, a heat transfer gas such as aHe gas may be supplied between an upper surface of the electrostaticchuck 18 and a rear surface of the semiconductor wafer W from a heattransfer gas supply mechanism (not illustrated) via a gas supply line34.

The susceptor 16 may be electrically connected to a first high frequencypower supply 36 and a second high frequency power supply 38 forattracting ions via lower matching units 40 and 42 and lower powersupply conductors 44 and 46, respectively. The lower power supplyconductors 44 and 46 may be configured as a common conductor such as apower supply rod.

The first high frequency power supply 36 may be configured to variablyoutput a first high frequency power RF_(L1) having a relatively lowfrequency of, for example, about 0.8 MHz suitable for attracting ions ofplasma to the semiconductor wafer W on the susceptor 16. The second highfrequency power supply 38 may be configured to variably output a secondhigh frequency power RF_(L2) having a relatively high frequency of, forexample, about 13 MHz suitable for attracting ions of plasma to thesemiconductor wafer W on the susceptor 16.

Above the susceptor 16, an upper electrode 48 may be provided so as toface the susceptor 16 in parallel with each other. This upper electrode48 may include an electrode plate 50 and an electrode support 52, andmay be secured at an upper space of the chamber 10 via a ring-shapedinsulator 54. The electrode plate 50 may have a multiple number of gasdischarge holes 50 a and may be made of a semiconductor material such asSi or SiC. The electrode support 52 may be made of a conductive materialsuch as aluminum whose surface is alumite-treated (anodically oxidized)for supporting the electrode plate 50 so as to be detachably attachedthereto. Between this upper electrode 48 and the susceptor 16, a plasmageneration space or a processing space PS is formed. The ring-shapedinsulator 54 may be made of, for example, alumina (Al₂O₃). Further, thering-shaped insulator 54 may airtightly fill up a gap between a sidesurface of the upper electrode 48 and a sidewall of the chamber 10, andphysically support the upper electrode 48 without being grounded.

The electrode support 52 may include a gas buffer room 56 therein and amultiple number of gas vent holes 52 a configured to communicate the gasbuffer room 56 with the gas discharge holes 50 a of the electrode plate50 at its lower surface. The gas buffer room 56 may be connected to aprocessing gas supply source 60 via a gas supply line 58, and a massflow controller (MFC) 62 and an opening/closing valve 64 may be providedat the gas supply line 58. If a certain processing gas is introducedinto the gas buffer room 56 from the processing gas supply source 60,the processing gas may be electrically discharged to the processingspace PS from the gas discharge holes 50 a of the electrode plate 50toward the semiconductor wafer W on the susceptor 16, as in a showerdevice. As described above, the upper electrode 48 may serve as a showerhead for supplying the processing gas to the processing space PS.

The upper electrode 48 may be electrically connected to a third highfrequency power supply 66 for plasma excitation via an upper matchingunit 68 and an upper power supply conductor such as a power supply rod70. The third high frequency power supply 66 may be configured tovariably output a third high frequency power RF_(H) having a frequencyof, for example, about 60 MHz suitable for high frequency discharge ofthe processing gas by capacitive coupling, i.e. suitable for generatingplasma. Typically, a frequency of the third high frequency power RF_(H)for generating plasma may be selected from a range of from about 27 MHzto about 300 MHz.

An annular space formed between the susceptor 16 and the sidewall of thechamber 10 and between the susceptor support 14 and the sidewall of thechamber 10 may serve as a gas exhaust space, and at the bottom of thisgas exhaust space, a gas exhaust port 72 of the chamber 10 may beformed. This gas exhaust port 72 may be connected to a gas exhaustdevice 76 via a gas exhaust line 74. The gas exhaust device 76 mayinclude a vacuum pump such as a turbo molecular pump and may beconfigured to depressurize the inside of the chamber 10, particularly,the processing space PS to a required vacuum level. At the sidewall ofthe chamber 10, a gate valve 80 configured to open and close aloading/unloading port 78 for the semiconductor wafer W may be provided.

An output terminal of a variable DC power supply 82 provided outside thechamber 10 may be electrically connected to the upper electrode 48 via aswitch 84 and a DC power supply line 85. The variable DC power supply 82may be configured to output a DC voltage V_(DC) ranging from, forexample, about −2000 V to about +1000 V.

A filter circuit 86 provided on the way of the DC power supply line 85may apply the DC voltage V_(DC) from the variable DC power supply 82 tothe upper electrode 48. Further, the filter circuit 86 may allow a highfrequency power supplied to the DC power supply line 85 from thesusceptor 16 via the processing space PS and the upper electrode 48 toflow through a ground line but not to flow toward the variable DC powersupply 82.

Further, at a certain place in contact with the processing space PSwithin the chamber 10, a DC ground part (not illustrated) made of aconductive material such as Si or SiC may be provided. This DC groundpart may be constantly grounded via a ground line (not illustrated).

A control unit 88 may include a micro computer and may individually andoverall control operations of respective parts of the plasma etchingapparatus, for example, the switch 24 for the electrostatic chuck, thefirst, second and third high frequency power supplies 36, 38 and 66, thematching units 40, 42 and 68, the processing gas supply unit 60, 62 and64, the gas exhaust device 76, the variable DC power supply 82 and theswitch 84 for DC bias, the chiller unit, and the heat transfer gassupply unit. Further, the control unit 88 may be connected to a touchpanel (not shown) serving as a man-machine interface and storage unit(not shown) for storing therein various program or data such as presetvalues. Furthermore, in the present embodiment, the control unit 88 anda DC controller 83 serve as a DC bias control unit.

In order to perform an etching process in this plasma etching apparatus,the gate valve 80 is opened, and the semiconductor wafer W as a targetto be processed is loaded into the chamber 10 and mounted on theelectrostatic chuck 18. Then, a certain processing gas, i.e. an etchinggas (generally, a mixed gas), may be introduced into the chamber 10 fromthe processing gas supply source 60 at a certain flow rate and a certainflow rate ratio. Then, the inside of the chamber 10 may be vacuumexhausted to a preset pressure level by the gas exhaust device 76.Further, the third high frequency power RF_(H)(60 MHz) for generatingplasma may be applied from the third high frequency power supply 66 tothe upper electrode 48 with a certain power level. Meanwhile, the firsthigh frequency power RF_(L1)(0.8 MHz) and second high frequency powerRF_(L2)(13 MHz) for attracting ions may be respectively applied from thefirst and second high frequency power supplies 36 and 38 with a certainpower level to the susceptor (lower electrode) 16. Then, the switch 24may be turned on, and a heat transfer gas (a He gas) may be confined ina contact interface between the electrostatic chuck 18 and thesemiconductor wafer W by electrostatic attraction force. Further, ifnecessary, the switch 84 may be turned on, and a certain DC voltageV_(DC) may be applied from the variable DC power supply 82 to the upperelectrode 48. The etching gas discharged from the shower head (upperelectrode) 48 may be excited into plasma between both electrodes 16 and48 by high frequency discharge, and a film on a main surface of thesemiconductor wafer W may be etched by radicals or ions contained in theplasma.

In order to control energy of ions which is incident onto thesemiconductor wafer W from the plasma during the process, the plasmaetching apparatus of this embodiment may include hardware 36 to 46 inwhich two kinds of high frequency powers RF_(L1)(0.8 MHz) and RF_(L2)(13MHz) suitable for attracting ions are applied to the susceptor 16 fromthe two high frequency power supplies 36 and 38. Further, the controlunit 88 may control a total power of both high frequency powers RF_(L1)and RF_(L2) and a power ratio thereof depending on specifications,conditions or recipes of an etching process.

[RF Bias Function in Embodiment]

In the plasma etching apparatus of the present embodiment, as describedabove, the first high frequency power RF_(L1)(0.8 MHz) and the secondhigh frequency power RF_(L2)(13 MHz) for attracting ions may be appliedto the susceptor (lower electrode) 16 from the first high frequencypower supply 36 and the second high frequency power supply 38,respectively, during the process. Then, as depicted in FIG. 2, anegative sheath voltage V_(S)(t) in which both high frequency powersRF_(L1) and RF_(L2) are applied may be generated in an ion sheath on asurface of the semiconductor wafer W or the susceptor 16 in contact withthe plasma generation space PS. FIG. 2 shows a case where a voltage(power) of the second high frequency power RF_(L2) is much lower than avoltage (power) of the first high frequency power RF_(L1) in order toeasily explain the application of the both high frequency powers RF_(L1)and RF_(L2) within the ion sheath.

Ions from the plasma may be accelerated by the sheath voltage V_(S)(t)and incident onto the surface of the semiconductor wafer W. In thiscase, acceleration or energy of the incident ions may depend on aninstantaneous value (absolute value) of the sheath voltage V_(S)(t) atthat moment. That is, ions introduced into the ion sheath when theinstantaneous value (absolute value) of the sheath voltage V_(S)(t) ishigh may be incident onto the surface of the wafer W with highacceleration or high kinetic energy, whereas ions introduced into theion sheath when the instantaneous value (absolute value) of the sheathvoltage V_(S)(t) is low may be incident onto the surface of the wafer Wwith low acceleration or low kinetic energy.

Herein, the ions within the ion sheath may respond (accelerate) to thesheath voltage V_(S)(t) with specific sensitivity equal to or less thanabout 100% (coefficient of 1). This response sensitivity or a conversionfunction α(f) may vary depending on (in inverse proportion to) afrequency f of a high frequency power used for RF bias as depicted inFIG. 3, and may be expressed by the following equation (1).

α(f)=1/{(cfτ _(i))^(p)+1}^(1/p)  (1)

Herein, c=0.3×2π, p=5, τ_(i)=3s (M/2 eV_(s)), M denotes a mass number ofions, s denotes a sheath passing time of ions, and V_(s) denotes asheath voltage.

Therefore, a net sheath voltage, i.e. an ion response voltage V_(i)(t),contributing to the acceleration of the ions within the ion sheath maybe expressed by the following equation (2).

V _(i)(t)=α(f)V _(S)(t)  (2)

FIGS. 2 and 3 respectively show the ion response voltage V_(i)(t) andthe conversion function α(f) of Ar⁺ ions. However, other ions may havethe same characteristics with respect to the sheath voltage V_(S)(t) andthe frequency for RF bias.

As can be seen from a voltage waveform of FIG. 3, the ions within theion sheath may respond (accelerate) to the first high frequency powerRF_(L1)(0.8 MHz) having a relatively low frequency with sensitivity ofabout 100% (α(f)≈1). Further, ions within the ion sheath may respond(accelerate) to the second high frequency power RF_(L2)(13 MHz) having arelatively high frequency with sensitivity of about 50% (α(f)≈0.5).

Based on the ion response voltage V_(i)(t) as described above, an ionenergy distribution (IED) can be calculated from the following equation(3) in the manner as depicted in FIGS. 4 and 5.

IED(E _(i))∝Σ_(i)(dV _(i) /dt _(i))  (3)

FIG. 4 shows an IED and an ion response voltage V_(i)(t) when a singlehigh frequency power having a relatively low frequency is used for RFbias. Meanwhile, FIG. 5 shows an IED and an ion response voltageV_(i)(t) when two high frequency powers each having a relatively lowfrequency or a relatively high frequency are used for RF bias.

In accordance with a single frequency bias method using a single highfrequency power for RF bias, as described above with reference to FIGS.19A to 19C and FIGS. 20A to 20C, regularly, an ion energy distribution(IED) has a shape that lots of ions are concentrated (peaks are shown)in the vicinity of the maximum energy and in the vicinity of the minimumenergy, and it may be impossible to vary the minimum energy as desiredeven if a RF power varies in any way.

In this regard, in accordance with a dual frequency bias method usingtwo high frequency powers RF_(L1)(0.8 MHz) and RF_(L2)(13 MHz) for RFbias in the same manner as the present embodiment, by adjusting a totalpower and/or a power ratio of both high frequency powers RF_(L1) andRF_(L2), it is possible to control the maximum energy and the minimumenergy in the ion energy distribution (IED) independently of each other.

That is, in the present embodiment, as depicted in FIGS. 6A to 6C, whilethe maximum energy is fixed to, for example, about 2000 eV, the minimumenergy can be adjusted in a range of, for example, from about 0 eV toabout 1000 eV as desired.

Further, as depicted in FIGS. 7A to 7C, while the minimum energy isfixed to, for example, about 350 eV, the maximum energy can be adjustedin a range of, for example, from about 650 eV to about 2650 eV asdesired.

FIGS. 6A to 6C and FIGS. 7A to 7C show the IED characteristics of Ar⁺ions, but other ions may have the same characteristics with respect tothe IED patterns. Further, each voltage value of the both high frequencypowers RF_(L1)(0.8 MHz) and RF_(L2)(13 MHz) corresponds to an amplitudevalue of each bias voltage of the both high frequency powers and may beconverted into RF powers.

In the present embodiment, as shown in FIG. 6B [RF_(L1)(0.8 MHz)=340 Vand RF_(L2)(13 MHz)=1000 V] and FIG. 7B [RF_(L1)(0.8 MHz)=500 V andRF_(L2)(13 MHz)=500 V], it may be possible to distribute ionssubstantially uniformly throughout the entire range of an energy band byusing dual frequency RF bias power. Further, as depicted in FIG. 7C[RF_(L1)(0.8 MHz)=1000 V and RF_(L2)(13 MHz)=500 V], it may be possibleto adjust the number of incident ions at an intermediate energy to begreater than the number of incident ions at the minimum energy and themaximum energy.

In the present embodiment, as depicted in FIG. 8A [RF_(L1)(0.8 MHz)=1500V and RF_(L2) (13 MHz)=0 V], FIG. 8B [RF_(L1)(0.8 MHz)=1125 V andRF_(L2)(13 MHz)=375 V], FIG. 8C [RF_(L1)(0.8 MHz)=750 V and RF_(L2)(13MHz)=750 V], FIG. 8D [RF_(L1)(0.8 MHz)=375 V and RF_(L2)(13 MHz)=1125V], and FIG. 8E [RF_(L1)(0.8 MHz)=0 V and RF_(L2)(13 MHz)=1500 V], itmay be possible to vary a width E_(W) of the energy band in a range of,for example, from about 1000 eV to about 3000 eV while an average valueor a central value of energy is fixed to, for example, about 1500 eV byusing the dual frequency RF bias power.

As described above, in the present embodiment, it may be possible toobtain intermediate IED characteristics by adjusting the width E_(W) ofthe energy band, as desired, between an IED characteristic (FIG. 8A)when only the first high frequency power RF_(L1)(0.8 MHz) for RF bias isused and an IED characteristic (FIG. 8E) when only the second highfrequency power RF_(L2)(13 MHz) for RF bias is used.

Among the intermediate IED characteristics, an IED characteristic ofFIG. 8B obtained when a power ratio of the second high frequency powerRF_(L2) to the first high frequency power RF_(L1) is 1125 V:375 V=3:1shows a distribution in a distinguishable concave shape. That is, ionsmay be concentrated in a band at the minimum energy and in the vicinitythereof (about 250 eV to about 750 eV) and at the maximum energy and inthe vicinity thereof (about 2250 eV to about 2750 eV). Meanwhile, fewerions may be distributed uniformly at an intermediate energy band (about750 eV to about 2250 eV). This concave-shaped IED characteristic may bedifferent from a U-shaped IED characteristic (FIGS. 8A and 8E) showingthat ions are concentrated on a narrow line at the minimum energy andthe maximum energy as in case where any one of the both high frequencypowers RF_(L1) and RF_(L2) for RF bias is used.

Although illustration is omitted, between FIG. 8D [RF_(L1)(0.8 MHz)=375V and RF_(L2)(13 MHz)=1125 V] and FIG. 8E [RF_(L1)(0.8 MHz)=0 V andRF_(L2)(13 MHz)=1500 V], i.e. when a power ratio of the second highfrequency power RF_(L2) to the first high frequency power RF_(L1) isabout 1:30, it may be possible to obtain an intermediate IEDcharacteristic of a concave shape in the same manner as shown in FIG.8B.

As described above, in the present embodiment, the first high frequencypower RF_(L1) and the second high frequency power RF_(L2) each having adifferent frequency may be used as a RF bias power. Further, a totalpower and/or a power ratio of these high frequency powers may beadjusted. Accordingly, an energy band width and a distribution shape ofthe ion energy distribution (IED) of the ions incident onto the surfaceof the semiconductor wafer W on the susceptor 16 can be controlled invarious ways.

The first high frequency power RF_(L1) and the second high frequencypower RF_(L2) are not limited to the above-described values (0.8 MHz and13 MHz, respectively), and can be set from a certain range as desired.As can be seen from a comparison between the IED characteristic of FIG.8A and the IED characteristic of 8E, in case of a single frequency biaspower, a width (an energy band) E_(W) of an ion energy distribution maybecome wider as a frequency becomes high and may become narrower as afrequency becomes low.

This relationship corresponds to a relationship between a frequency anda conversion function α(f) as depicted in FIG. 9. Therefore, in order toincrease a variable range of the energy band width E_(W), it depends ona kind of an ion (F⁺, Ar⁺, C₄F₆ ⁺ or the like) mainly acting in anetching process. However, basically, the first high frequency powerRF_(L1) needs to have a relatively low frequency (for example, about 100kHz to about 6 MHz) and the second high frequency power RF_(L2) needs tohave a relatively high frequency (for example, about 6 MHz to about 40MHz). In particular, if a frequency of the second high frequency powerRF_(L2) is too high, that is, the frequency is greater than about 40MHz, it may become inappropriate for RF bias due to its strong effect ofplasma generation. Thus, the second high frequency power RF_(L2) needsto have a frequency of about 40 MHz or lower.

[Experimental Example of Process]

As described above, the plasma etching apparatus of the presentembodiment can remarkably improve controllability of a RF bias function,and in particular, high performance in anisotropic etching can beachieved as compared with the conventional apparatus.

Herein, as an appropriate etching process performed by the plasmaetching apparatus of the present embodiment, a HARC (High Aspect RatioContact) process will be explained with reference to FIG. 10. The HARCprocess may be an etching process for forming a narrow and deep contacthole (or a via hole) 92 in an insulating film or an oxide film(typically, a SiO₂ film). Further, the HARC has been used for contactetching (or via hole etching) for a BEOL (Back End of Line) in amanufacturing process of a large-scale integrated circuit.

In the HARC process, an anisotropic shape of high precision and a highselectivity with respect to a mask 94 (and an underlying film 96) may berequired in order to form the fine hole 92 of a high aspect ratio. Forthis reason, there has been used a method of performing a verticaletching process by vertically attracting ions such as CF_(X) ⁺ or Ar⁺into the hole 92 of the SiO₂ film 90 by RF bias while afluorocarbon-based gas is used as an etchant gas and a polymer film as asidewall protective film is deposited on the mask 94 and a sidewall 98of the hole 92 of the SiO₂ film 90 with CF_(X) radicals. In this case,since F radicals having chemically high activity may reduce anisotropyand selectivity, a gas such as C₄F₈, C₅F₈ or C₄F₆ generating fewer Fradicals and having a high C/F ratio has been widely used.

In this HARC process, in order to increase an etching rate of the SiO₂film, (1) an increase in amount of incident ions, (2) an increase intotal amount of F in radicals, and (3) sufficient ion energy may berequired. To satisfy the requirement (1), [1] a method of adjusting ahigh frequency power for generating plasma has been employed; to satisfythe requirement (2), [2] a method of adjusting a flow rate of afluorocarbon gas (for example, C₄F₈) has been employed; and to satisfythe requirement (3), [3] a method of adjusting a high frequency powerfor attracting ions has been employed.

Further, in order to increase selectivity of the SiO₂ film 90 withrespect to the mask 94 (and the underlying film 96), (4) an appropriateflow rate ratio of O₂/C₄F₈, and (5) an increase in total gas flow ratecaused by addition of Ar may be required. To satisfy the requirement(4), [4] a method of adjusting a flow rate of an O₂ gas has beenemployed, and to satisfy the requirement (5), [5] a method of adjustinga flow rate of an Ar gas has been employed.

The requirements (4) and (5) related to the selectivity may be based onthe following etching mechanism. That is, in a normal etching state,fluorocarbon radicals are constantly irradiated onto a surface of a SiO₂film, and thus, a CF film having multi-molecular layers may be formed onthe surface of the SiO₂ film. A thickness of this CF film may have aclose relationship with an etching rate.

FIGS. 11A and 11B show that, in case of using a mixed gas of C₄F₈/Ar/O₂as an etching gas, each etching rate of a SiO₂ film and a SiN film, andthicknesses of CF polymer films deposited on these films while a flowrate of a C₄F₈ gas is varied and a flow rate of each of an Ar gas and anO₂ gas is fixed.

As depicted in FIG. 11A, in an etching process for the SiO₂ film, as aflow rate of the C₄F₈ gas is increased, an etching rate (E/R) isincreased up to about 11 sccm as a maximum value. Thereafter, theetching rate (E/R) is decreased in inverse proportion to an increase ina thickness of the CF film, and is scarcely changed at about 22 sccm ormore. In this case, when the flow rate of the C₄F₈ gas is about 11 sccm,the thickness of the CF film on the SiO₂ film is as thin as about 1 nmsince oxygen released during the etching process for the SiO₂ filmreacts with the CF film and produce a volatile material (i.e. remove theCF film).

As depicted in FIG. 11B, in an etching process for the SiN film,nitrogen is released instead of oxygen. However, since the nitrogen ismuch less capable of removing the CF film as compared with the oxygen, athickness of the CF film on the SiN film is as thick as about 5 nm, sothat the etching can be suppressed.

In both etching processes for the SiO₂ film and the SiN film, the O₂ gasas an additive gas may adjust a removing rate of the CF film.

In the HARC process, a SiN film may be used as the underlying film 96and typically, an organic film may be used as the mask 94. With respectto an etching rate and a thickness of the CF film when a flow rate ofthe C₄F₈ gas is varied under the same conditions as described above, thesame characteristics as the SiN film can be seen in a case where theorganic film is used as the mask 94.

As described above, in order to increase the selectivity of the SiO₂film, it is possible to use a difference in a thickness of the CF film(a difference in an etching rate) based on whether or not oxygen isreleased during an etching process or based on a difference in amount ofreleased oxygen. Further, in order to increase the selectivity of theSiO₂ film, [4] a flow rate ratio of O₂/C₄F₈ may be adjusted, and also[5] F atom radicals that deteriorates the selectivity may be reduced byaddition of Ar (i.e. a total gas flow rate is increased). Accordingly,it may be possible to sufficiently increase the selectivity of the SiO₂film with respect to the SiN film as the underlying film 96 or theorganic film (which may include photoresist as an upper layer) as themask 94.

As described above, in a typical plasma etching apparatus, by usingrespective methods of adjusting [1] a high frequency power forgenerating plasma, [2] a flow rate of a fluorocarbon gas (for example,C₄F₈), [3] a high frequency power for attracting ions, [4] a flow rateratio of O₂/C₄F₈ (particularly, a flow rate of O₂), and [5] a flow rateof Ar, it may be possible to achieve a high etching rate and highselectivity in a HARC process. However, since very high selectivity isrequired in the HARC process, a very high deposition rate needs to beconsidered, so that radicals having a high adhesion rate needs be used.

In this case, as depicted in FIG. 12B, coatability (coverage) of adeposition film 100 on the sidewall 98 may deteriorate and an entranceof the hole 92 may become narrow, and, thus, a necking 100 may be causedeasily. If the necking 100 is caused, radicals or ions may not besufficiently attracted to the bottom of the hole 92. Therefore, adecrease in a CD (Critical Dimension) of the bottom of the hole or adecrease in a vertical etching rate of the hole bottom. Further,incident ions may be reflected from an upper portion of the necking 100,and a bowing of the sidewall 98 may occur in a lower portion of thenecking 100.

As described above, in order to achieve high selectivity, it may benecessary to use radicals having a high adhesion rate (C_(x)F_(y)radicals), but such radicals may easily cause the necking 100. However,if radicals having a low adhesion rate are used to avoid the necking100, the deposition film 100 on the mask 94 may become too thin asdepicted in FIG. 12A and thus high selectivity cannot be achieved.

As described above, there is a trade-off relationship between a blanketcharacteristic (an etching rate and selectivity) and an etching profilein the HARC process. Thus, it is impossible to solve this trade-offproblem by the conventional RF bias technology using a high frequencypower having a single frequency for attracting ions.

FIG. 13A shows etching yield characteristics of an oxide film (SiO₂) andan organic film with respect to energy of incident ions when radicalshaving a high adhesion rate are used in a HARC process. As describedabove, if the radicals having a high adhesion rate are used, a surfaceof the mask (organic film) may be protected by a deposition film at alow ion energy band and only the oxide film may be selectively etched.In addition, if the ion energy band becomes higher than a certainthreshold value E_(t), physical etching by means of irradiation of ionsexceeds the protection of the deposition film, and, thus the mask(organic film) becomes etched. As the energy of the incident ions isincreased, the etching yield of the oxide film is increased slowly.

In order to increase selectivity, an ion energy distribution need tohave a shape where ions are concentrically distributed at an energy bandnear the threshold value E_(t), as shown in FIG. 13B. However, inaccordance with the conventional single frequency RF bias method (thesingle frequency bias method), an ion energy distribution is arrangedentirely in a range lower than the threshold value E_(t). In this case,ions concentrated in the vicinity of the minimum energy may hardlycontribute to the etching for the oxide film. Even though highselectivity may be achieved by means of ions concentrated in thevicinity of the maximum energy, the above-described necking 100 cannotbe avoided or prevented.

In a HARC process as depicted in FIG. 15, the present inventors havefound the following fact by comparing etching yield characteristics withrespect to ion energy at a position (an upper surface of the mask) wherean incident angle θ to a normal line N of a surface of an organic filmis about 0° and at a position (an inclined surface 102 of the necking)where the incident angle θ to the normal line N of the surface of theorganic film is about 80°. That is, as depicted in FIG. 14A, an etchingyield at the upper surface of the mask (θ=0°) may be shown earlier thanan etching yield at the necking (θ=80°). However, if energy of incidentions exceeds a certain value Es, the inclined surface 102 of the necking(θ=80°) may become easier to be etched than the upper surface of themask (θ=0°). That is, the upper surface of the mask may be etched byions, but the inclined surface 102 of the necking may be etched moreefficiently. Accordingly, it is possible to increase a CD of thenecking.

In view of the etching yield/ion energy characteristics of the oxidefilm and the organic film (mask) in the HARC process, as depicted inFIG. 14B, it can be seen that it is desirable to have a concave-shapedIED characteristic having a peak at a first energy band which is in thevicinity of the threshold value E_(t) and lower than the threshold valueE_(t) and having a peak at a second energy band which is in the vicinityof the certain value E_(s) and higher than the certain value E_(s).

That is, ions are distributed concentrically at the first energy band,so that high selectivity can be obtained. Further, ions are distributedconcentrically at the second energy band, so that the necking 100 can beefficiently avoided or prevented.

If the ions are concentrated at an intermediate energy band between thefirst energy band and the second energy band, selectivity may not beincreased and the necking may not be avoided. Accordingly, fewer ionsneed to be distributed in this intermediate energy band.

The present inventors have conducted an experiment of the HARC processby the plasma etching apparatus of the present embodiment while varyinga power ratio of the first high frequency power RF_(L1)(0.8 MHz) and thesecond high frequency power RF_(L2)(13 MHz) and comparing the relevantetching characteristics. Experiment results as shown in FIGS. 16 and 17are obtained. In this case, main etching conditions are as follows:

Diameter of wafer: 300 mm

Etching gas: C₄F₆O₂=60/200/60 sccm

Internal Pressure of chamber: 20 mTorr

Temperature: upper electrode/sidewall of chamber/lowerelectrode=60/60/20° C.

High frequency power:

high frequency power for generating plasma (60 MHz)=1000 W

high frequency power for attracting ions (13 MHz/0.8 MHz)=4500/0 W,4000/500 W, 3000/1500 W, 2000/2500 W, 1000/3500 W, 0/4500 W (sixexamples)

DC voltage: V_(DC)=−300 V

Etching time: 2 minutes

In this experiment, a total power of the first high frequency powerRF_(L1)(0.8 MHz) and the second high frequency power RF_(L2)(13 MHz) forattracting ions has been fixed (at about 4500 W). Further, a power ratioas a parameter has been selected from six examples from 4500/0 W to0/4500 W.

As desirable etching characteristics in the HARC process, an etchingrate of the SiO₂ film needs to be high, selectivity of the mask needs tobe high, a difference between a necking CD and a bowing CD needs to besmall, and an inclined angle of the sidewall of the mask needs to behigh. From this point of view, it can be seen that when the first highfrequency power RF_(L1) and the second high frequency power RF_(L2) areset to be about 1000 W and about 3500 W, respectively, excellent etchingcharacteristics have been achieved as a whole. In this case, a powerratio of the both high frequency powers RF_(L1) and RF_(L2) may be about3.5:1, and although illustration is omitted, the same concave-shaped IEDcharacteristic as shown in FIG. 8B has been obtained.

As described above, in accordance with the dual frequency bias method ofthe present disclosure, the trade-off problem in the HARC process can bereadily solved. Further, in accordance with the dual frequency biasmethod of the present disclosure, it may be also possible to solve atrade-off between selectivity and a top CD/a bowing CD/a bottom CD in anetching process for forming a hole and a trade-off between a depositionrate and a seamless shape in plasma CVD.

Furthermore, the concave-shaped IED characteristic achieved by the dualfrequency bias method of the present disclosure may have an effect inthe HARC process. However, a flat-shaped IED characteristic (FIGS. 6B,7B and 8C) or a mountain-shaped IED characteristic (FIG. 7C) achieved bythe dual frequency bias method of the present disclosure may be adistinctive characteristic. These characteristics cannot be achieved bythe conventional single frequency bias method and may optimize a certainprocess characteristic.

[DC Bias Function in Embodiment]

In the plasma etching apparatus of the present embodiment, by turning ONthe switch 84 if necessary, the DC voltage V_(DC) from the variable DCpower supply 82 is applied to the upper electrode 48. As describedabove, by applying to the upper electrode 48 the appropriate DC voltageV_(DC), particularly, the DC voltage V_(DC) having an appropriatemagnitude (absolute value), etching resistance of a photoresist film(particularly, an ArF resist film) used as a mask in the plasma etchingprocess can be improved.

That is, if the DC voltage V_(DC) as a negative high voltage (desirably,a negative voltage having an absolute value higher than an absolutevalue of a self-bias voltage generated on the upper electrode 48 byapplying the third high frequency power RF_(H)) is applied to the upperelectrode 48 from the variable DC power supply 82, an upper ion sheathformed between the upper electrode 48 and the plasma may become thick.Accordingly, ions in the plasma are accelerated in an electric field ofthe upper ion sheath, and, thus, ion impact energy when the ions collidewith the electrode plate 50 of the upper electrode 48 may be increased.As a result, secondary electrons released from the electrode plate 50 bya γ electric discharge may be increased. The secondary electronsreleased from the electrode plate 50 may be accelerated in a directionopposite to the direction of the ions in the electric field of the upperion sheath, and may pass through the plasma PR. Thereafter, thesecondary electrons pass through a lower ion sheath and then may beintroduced, with a certain high energy, into a resist mask on thesurface of the semiconductor wafer W on the susceptor 16. If a polymerof the resist mask absorbs the energy of the electrons, a change incomposition or structure and a cross-linking reaction may be made. As aresult, a modification (reform) layer may be formed and the etchingresistance (plasma resistance) may be increased. As the absolute valueof the negative DC voltage V_(DC) applied to the upper electrode 48 isincreased, the energy of the electrons introduced into the resist maskcan be increased, and the etching resistance in the resist mask can alsobe increased.

Meanwhile, in the plasma etching apparatus of the present embodiment, asdescribed above, by applying to the susceptor 16 the first highfrequency power RF_(L1) and the second high frequency power RF_(L2) eachhaving a different frequency as RF bias powers and by controlling thetotal power and/or the power ratio of these high frequency powers, inthe ion energy distribution (IED) of the ions incident onto the surfaceof the semiconductor wafer W on the susceptor 16, the width of theenergy band, the distribution shape and the total amount of ion incidentenergy can be controlled in various manners. In particular, if the firsthigh frequency power RF_(L1) and the second high frequency power RF_(L2)are appropriately selected and combined with each other, the number ofincident ions at the intermediate energy band in the ion energydistribution (IED) may be rapidly increased. Accordingly, the totalamount of ion incident energy can be increased. However, if the totalamount of ion incident energy is increased, the resist mask may bedamaged, so that a surface of the resist mask may become rough. Further,uneven deformation or zigzag-shaped deformation of so-called LER (LineEdge Roughness) or LWR (Line Width Roughness) may easily occur.

Therefore, in the present embodiment, the control unit 88 may calculate(estimate roughly) the total amount of ion incident energy based on thetotal power and the power ratio of the first high frequency powerRF_(L1) and the second high frequency power RF_(L2) If the total amountof ion incident energy is large, the control unit 88 may increase,through the DC controller 83, the absolute value of the negative DCvoltage V_(DC) applied to the upper electrode 48 so as to improve theetching resistance of the resist mask. However, if the total amount ofion incident energy is small, it is preferable to control the absolutevalue of the negative DC voltage V_(DC) applied to the upper electrode48 to be small for the reason that needs for improving the etchingresistance of the resist mask are decreased and for the followingreason.

That is, in the plasma etching apparatus of the present embodiment, by ahigh frequency discharge of the etching gas, a fluorocarbon gas(C_(x)F_(y)) is dissociated and reactant species such as F atoms or CF₃are produced. These reactant species react with a process target film onthe surface of the semiconductor wafer W, so that a volatile product(for example, SiF₄) is produced and a polymer film (for example,(CF₂)_(n)) serving as a deposition film is also produced. If theelectrode plate 50 of the upper electrode 48 is made of a conductivematerial containing Si, the same reaction may occur on a surface of theelectrode plate 50 as well as the surface of the semiconductor wafer W,and, thus, the reactant species may be consumed on the both surfaces. Atthis time, if the negative DC voltage V_(DC (≦)0 V) is applied to theupper electrode 48, an etching reaction (i.e. consumption of thereactant species) on the surface of the electrode plate 50 may beaccelerated by means of an ion-assist effect and a large amount ofC-rich CFx may be produced. As a result, an etching rate on the surfaceof the semiconductor wafer W can be decreased and the deposition may beincreased. As the absolute value of the negative DC voltage V_(DC) isincreased, the ion-assist effect on the surface of the electrode plate50 may be increased. Accordingly, based on the above-described reaction,the etching rate on the surface of the semiconductor wafer W can befurther decreased and the deposition can be further increased. Thesedecrease of the etching rate and the increase of the deposition may notbe desirable if the total amount of energy of the ions incident onto thesurface of the semiconductor wafer W on the susceptor 16 is small.Therefore, in this case, the control unit 88 controls, through the DCcontroller 83, the absolute value of the negative DC voltage V_(DC)applied to the upper electrode 48 to be relatively low.

Another Embodiment or Modification Example

In the above-described embodiment, the third high frequency power RF_(H)for generating plasma output from the third high frequency power supply66 has been applied to the upper electrode 48. As another embodiment, asdepicted in FIG. 18, the third high frequency power supply 66 and thematching unit 68 may be electrically connected to the susceptor (lowerelectrode) 16 and the third high frequency power RF_(H) for generatingplasma may be applied to the susceptor 16.

The above-described embodiment is related to a capacitively coupledplasma processing apparatus in which plasma may be generated by highfrequency discharge between parallel plate electrodes in a chamber.However, the present disclosure may be applied to an inductively coupledplasma etching apparatus in which plasma may be generated under aninductive electromagnetic field of a high frequency power by arrangingan antenna on an upper surface of a chamber or around the chamber.Further, the present disclosure may be applied to a microwave plasmaprocessing apparatus in which plasma may be generated by using a powerof microwave.

The present disclosure is not limited to a plasma etching apparatus andcan be applied to other plasma processing apparatus for plasma CVD,plasma oxidation, plasma nitrification, sputtering or the like. Further,the target substrate of the present disclosure is not limited to asemiconductor wafer and may include various substrates for a flat paneldisplay, an EL device or a solar cell, or a photomask, a CD substrate,or a print substrate.

What is claimed is:
 1. A plasma processing apparatus comprising: anevacuable processing chamber for accommodating a target substrate havingthereon an oxide film and an organic film and for loading/unloading thesubstrate; a processing gas supply unit for supplying a processing gasinto the processing chamber; a plasma generation unit for generatingplasma of the processing gas within the processing chamber; a firstelectrode for mounting and holding the substrate thereon within theprocessing chamber; a first high frequency power supply unit forapplying to the first electrode a first high frequency power having afirst frequency in order to attract ions from the plasma toward thesubstrate on the first electrode; a second high frequency power supplyunit for applying to the first electrode a second high frequency powerhaving a second frequency higher than the first frequency in order toattract ions from the plasma toward the substrate on the firstelectrode; and a control unit for controlling a minimum energy and amaximum energy of the ions incident onto the substrate independently ofeach other such that ion energy of the ions are concentrated at a firstenergy band and a second energy band respectively, wherein the oxidefilm is etched using the organic film as a mask to form a hole withinthe oxide film by the plasma, the first energy band is lower than afirst energy value at which the oxide film is etched while the organicfilm is not etched, and the second energy band is higher than a secondenergy value at which an etching yield at an inclined surface of thehole is higher than an etching yield of an upper surface of the organicfilm.
 2. The plasma processing apparatus of claim 1, wherein the firstfrequency is in a range of from about 100 kHz to about 6 MHz, and thesecond frequency is in a range of from about 6 MHz to about 40 MHz. 3.The plasma processing apparatus of claim 1, wherein the plasmageneration unit includes: a second electrode provided to face the firstelectrode in parallel with each other at a distance therebetween withinthe processing chamber; and a third high frequency power supply unit forapplying to the first electrode or the second electrode a third highfrequency power having a third frequency higher than the secondfrequency in order to electrically discharge the processing gas.
 4. Theplasma processing apparatus of claim 3, wherein the third frequency isin a range of from about 27 MHz to about 300 MHz.
 5. The plasmaprocessing apparatus of claim 3, further comprising: a variable DC powersupply for applying to the second electrode a negative DC voltage; and aDC bias control unit for controlling an absolute value of the negativeDC voltage depending on a total power and a power ratio of the first andsecond high frequency powers.
 6. The plasma processing apparatus ofclaim 5, wherein the DC bias control unit includes: a calculation unitfor calculating a total amount of energy of the ions incident onto thesubstrate based on the total power and the power ratio of the first andsecond high frequency powers; and a controller for controlling theabsolute value of the negative DC voltage to be increased as much as thetotal amount of energy is increased and the absolute value of the DCvoltage to be decreased as much as the total amount of energy isdecreased.